The invention relates to a hydraulic power steering for motor vehicle with a servo valve in the form of a rotary spool valve having control components which are rotatable relative to each other and interconnected by spring means, preferably a torsion rod which retains them in a normal relative position and with a steering gear arrangement which is connected to the steered vehicle wheels and to a hydraulic servo motor controlled by the servo valve.
Power steering systems are generally known and are installed in mass produced vehicles. Usually, a control element, that is, a steering wheel is operatively coupled to the steering gear structure wherein the rotary servo valve is part of the drive connection between the steering wheel and the steering gear structure. Depending on the torque effective between the steering wheel and steering gear structure, the servo valve is displaced in one or the opposite direction whereby the hydraulic servo motor is so controlled that it provides a servo force supporting the steering maneuver so that the manual force needed to operate the steering wheel is reduced.
It is also known basically to operate with the control element only a setting means which then cooperates via a control circuit, with an operating motor, whose control actions are adjusted by a set value--actual position comparison so that the control actions essentially correspond to the movement of the control element. Such control concepts with electronic control circuits are used for example in air planes for the operation of the wing flaps, the elevators and the rudders. These control arrangements, which are also called fly-by-wire controls, have achieved in the meantime such a good safety record that they are used not only in military aircraft but also in commercial passenger air planes.
It is the object of the present invention to utilize such a concept also for motor vehicles and utilize in connection therewith as many proven conventional power steering parts as possible.